The present invention relates to a power ON-OFF control circuit and, more particularly, to a power the ON-OFF control circuit for controlling ON-OFF states of a power source such as a relatively small capacity power source which drives an electronic apparatus including a memory.
A power ON-OFF control circuit as shown in FIG. 1 is generally used for controlling the ON-OFF states of a power source. The power ON-OFF control circuit of FIG. 1 includes a power transformer T1, a rectifying diode D1, smoothing condensors C1 and C2, a current control transistor Tr1, a Zener diode D2, a resistance R1, a condensor C3, and a switching transistor Tr2.
A power stabilizing circuit in series comprises the power transformer T1, the rectifying diode D1, the smoothing condensors C1 and C2, the current control transistor Tr1, the Zener diode D2, the resistance R1, and the condensor C3 all operated to stabilize the power from the power source. The switching transistor Tr2 is inserted and connected between the base of the current control transistor Tr1 and the ground, and the switching transistor Tr2 operates to control the ON-OFF states of the power source based on the operation of the above-described power stabilizing circuit.
The power ON-OFF control circuit is connected to an AC (Alternating Current) power source through an AC plug P, and further, connected to a load L to which the power is applied from the AC power source. The power from the AC power source is switched on or off by a main power switch SW1.
The operation of the power ON-OFF control circuit of FIG. 1 will be described below.
When the main power switch SW1 is switched on, an "L" (Low) level control signal is applied to the base of the switching transistor Tr2, so that the switching transistor Tr2 is placed in the OFF state and the current control transistor Tr1 is placed in the ON state. Therefore, a rectifying output voltage Vcc1 at the collector of the current control transistor Tr1 is stabilized by the current control transistor Tr1 and transformed into a DC (Direct Current) voltage Vcc2, and the stabilized DC voltage Vcc2 is further applied to the load L.
When the main power switch SW1 is switched off, a "H" (High) level control signal is applied to the base of the switching transistor Tr2, so that the switching transistor Tr2 is placed in the ON state and the current control transistor Tr1 is placed in the cut-off state. Therefore, the rectifying output voltage Vcc1 is cut off by the current control transistor Tr1 and the DC voltage Vcc2 is not applied to the load L.
However, in the case where the AC plug P is pulled out or the main power switch SW1 is switched off while the "L" level control signal is applied to the base of the switching transistor Tr2, in other words, while the main power switch SW1 is switched on, the DC voltage Vcc2 applied to the load L is gradually decreased as being dependent on the decrease of the rectifying output voltage Vcc1 while the current control transistor Tr1 is continuously placed in the ON state. Because the rectifying output voltage Vcc1 is decreased with small vibration, the DC voltage Vcc2 is gradually decreased with small vibration, also.
If the load L includes a memory such as a semiconductor memory, the memory may be caused to malfunction by the vibration of the DC voltage Vcc2, or the memory contents of the memory may be destroyed.